The present invention relates to a system and method for limiting power drawn by a load. More particularly, the invention relates to a system and method for actively limiting the electric power drawn from a power distribution bus by one or more electric motor loads.
Electric motor loads are installed and utilized in various environments in which size, weight, and cost are limiting variables. For example, modern aircraft, both for commercial and military applications, are now being designed with electrically powered actuation systems. Such actuation systems increase the electric load on the aircraft""s main electric power distribution system. The electric power demand of electric actuation systems is determined by actuator speed and the load on the actuator. It is difficult, however, to design the power distribution system for the fall range of load that the actuators may naturally encounter over the entire operating envelope of the aircraft. Hence, to ensure that the power distribution system can provide the needed power to the actuators over the entire operating envelope, including both normal load and unusually high load transients, the power generation and distribution system must be designed with a sufficiently conservative design margin.
Although a conservative design margin provides for a rather robust power generation and distribution system, it also results in increased size, weight, and cost in the manufacture of the aircraft. Moreover, the components that make up the controllers for the actuation system motors need to be robustly designed to meet the conservative design power requirements, which also increases size, weight, and cost.
Hence, there is a need for a system and method for limiting the power that is drawn from a main power distribution bus by one or more electric motor loads that solves at least the above-described problems. Namely, a system and method for actively limiting the power drawn from the main power distribution bus by one or more electric motor loads so that the required design capacity of both the generation and distribution system, and the motor controllers, can be reduced, resulting in reduced size, weight, and cost.
In one embodiment of the present invention, a control system for actively limiting the power drawn from a power distribution bus by one or more electrical loads to a predetermined maximum power level includes current based power limit determination means and power limiting means. The current based power limit determination means receives at least a signal representative of a voltage magnitude supplied to the one or more electrical loads, determines a maximum permissible current magnitude, based on the received signal, that may be supplied to the one or more electrical loads from the power distribution bus to prevent the electrical power drawn therefrom from exceeding the predetermined maximum power level, and generates a power limited current command signal based on the determined maximum permissible current magnitude. The power limiting means, in response to the power limited current command signal, limits the power drawn from the power distribution bus to the maximum permissible power level.
In another aspect of the present invention, a control system for actively limiting electrical power drawn from a power distribution bus by one or more electrical loads to a predetermined maximum power level includes voltage based power limit determination means and power limiting means. The voltage based power limit determination means receives at least a signal representative of a current magnitude supplied to the one or more electrical loads, determines a maximum permissible voltage magnitude, based on the received signal, that may be supplied to the one or more electrical loads from the power distribution bus to prevent the electrical power drawn therefrom from exceeding the predetermined maximum power level, and generates a power limited voltage command signal based on the determined maximum permissible voltage magnitude. The power limiting means, in response to the power limited voltage command signal, limits the power drawn from the power distribution bus to the maximum permissible power level.
In yet a further aspect of the present invention, a control system for actively limiting electrical power drawn from a power distribution bus by one or more electrical loads to a predetermined maximum power level includes current based power limit determination means, voltage command determination means, voltage based power limit determination means, and power limiting means. The current based power limit determination means receives at least a signal representative of a voltage magnitude supplied to the one or more electrical loads, determines a maximum permissible current magnitude, based on the received signal, that may be supplied to the one or more electrical loads from the power distribution bus to prevent the electrical power drawn therefrom from exceeding the predetermined maximum power level, and generates a power limited current command signal based on the determined maximum permissible current magnitude. The voltage command determination means receives the power limited current command signal and a signal representative of a current magnitude supplied to the one or more electrical loads, determines a voltage magnitude to be supplied to the one or more electrical loads from the power distribution bus, and generates a voltage command signal. The voltage based power limit determination means receives at least the voltage command signal and a signal representative of a current magnitude supplied to the one or more electrical loads, determines a maximum permissible voltage magnitude, based on the received current magnitude signal, that may be supplied to the one or more electrical loads from the power distribution bus to prevent the electrical power drawn therefrom from exceeding the predetermined maximum power level, and generates a power limited voltage command signal based on the determined maximum permissible voltage magnitude. The power limiting means, in response to the power limited voltage command signal, limits the power drawn from the power distribution bus to the maximum permissible power level.
Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.